On Thu, 6 Jun 2013, Jonathan McDowell wrote: > On Wed, May 22, 2013 at 05:14:18PM -0400, Mikulas Patocka wrote: > > > This is updated dm-switch. It has better documentation and better error > > reporting in message function. > ... > > --- > > > > From: Jim Ramsay <jim_ramsay@xxxxxxxx> > > > > dm-switch is a new target that maps IO to underlying block devices > > efficiently when there are a large number of fixed-sized address regions > > but there is no simple pattern to allow for a compact mapping > > representation such as dm-stripe. > > Interesting. I have been working on something similar recently, for not > dissimilar reasons. However the approach I had been taking was to extend > __choose_pgpath to take a pos parameter indicating the block being > requested, and then add a new dm-pref-hint multipath driver, which > effectively does a round-robin but prefers any path that has the "pref" > bit. Currently the dm-pref-hint driver is extremely hacky and reaches > down into the scsi_device to do an appropriate CDB along each path to > get the pref-map, or I'd post it for comments. > > I'm interested in why the decision was made to have dm-switch as a separate > device-mapper layer? Are there a corresponding set of patches to > multipath-tools which know how to do the setup of each individual path? > > J. It is a separate target because it was originally developed as such by Dell. It could be possible to turn it into a plugin to dm-mpath but that would require changes in the userspace code that is driving it. Mikulas -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
